Preparation of Low Loss Mn-Zn Ferrites for High Frequencies Through an Oxalate Precipitation Process

摘要

Low loss Mn-Zn ferrites for high frequency power applications (f> 500 khz) were synthesized through an oxalate synthesis route. Mn-Zn-Fe oxalates were precipitated at room temperature. After thermal decomposition at 500°C ferrite powders with a particle sizes of 50 nm were obtained. For comparison, ferrites were prepared by a standard oxide process. Powders calcined at 1030°C were fine milled; a particle size of 50 nm was reached after cascade milling. The ferrite/haematite powder formed during calcination transforms into a single spinel ferrite on high-energy ball milling. Compaction of the nanopowders results in green densities > 2.5 g/cm3. Sintering at 1150°C leads to homogeneous microstructures with a density of 5.1 and 4.9 g/cm3 for ferrites from the oxalate and oxide milling processes, respectively. Low power losses were measured for Mn-Zn ferrites from both routes, e.g. 65 mW/cm3 (500 kHz, 50mT, 80°C) and 55-80 mW/cm3 (1MHz, 25mT, 80°C).